The speeds and feed charts that are glued to the insides of the units are considered best used as a guide. Once you get into the general ball park you need to adjust your wire feed and travel speed based on weld penetration and getting complete fusion of the parent materials. When you are watching the weld puddle develop on a MIG you are looking for a weld puddle that appears much the same as a stick welder. The puddle will generally be smaller and a little more difficult to see, but you are looking for the parent matals at the base of the groove, notch or Vee to become molten and flow into each other and the filler wire. As you progress across the length of the weld you need to consider warping and pulling out of alignment. Sometimes you have to stop on one side and weld on the other side to retain the alignment that the part is designed for. Also you sometimes have to stop and move to a different location along the weld and stitch there for some distance and repeat this until you have made several short welds along the length of the weld. Then you go back and repeat the procedure again until you have created a continuous homogenous weld from end to end. This will also be repeated on the back side of the weld depending on what the engineer has placed on the weld specifications on the drawing. Only one side, both sides, interrupted, bead profile and diameters are all spelled out on the drawing. If you are not working from a drawing, then you will have to decide how you wish to weld the item to get 100% base metal fusion and not a pretty weld bead that is just piled up on the joint but contributes no structural strength at all. Once you get your machine perking along you should listen and the weld filler and the weld will have a unique sound that is very similar to the sound of frying eggs. This usually indicates that your speed and wire feed rate are pretty darn close and all you need to do at that point is insure that the weld is actually penetrating the material and fusing it together. Otherwise you end up with that pretty bead that does nothing. As you gain a little more experience I would weld 2 pieces of material together and do a bend test on them to see exactly what I am talking about. On a proper weld you cannot separate the material at the weld, the metals adjacent to the weld should fail first. The cut and etch method will also disclose the size and depth of your weld nugget and show you exactly how well you fused that material. It takes a bit of time to do those "test" but it will be time well spent to discover just how well you are performing against the standard. Hope this helps you understand the use of speed and feed on wire welders such as the 150. I have a MM 210 that will do 3/8ths material in one pass, but that is a 210 amp machine running wide open with the dials all set to "kill" and my duty cycle drops off to below 20% when I run the machine like that. So I have to stop constantly to allow the machine to cool off or it will overheat and damage the windings inside the machine. Hope this helped get you pointed in the right direction and do not hesitate to ask any question you may ever have because ther are several of us retired welders who will be glad to explain it and help guide you to get the best performance from your welds and your machine. The MM 150 is a really nice and pretty tough little machine when it is used within it's design limits.
Bob
